For what I understand in the question, the "big number" is called a <em>stoichiometric coefficient </em>and represents the ammount of molecules of the substance that follows it ( in this case O2) involved in a reaction.
In this case there is no reaction but it asks you for the lewis structure of two molecules of oxygen (O2).
The lewis structure of oxygen is: O=O
<u>Two molecules of it can bond by london forces or dative unions forming what is known as a dimer</u> (two molecules of the same substance bonded).